1. Field of the Invention
The present invention relates to apparatus for reproducing a still picture from parallel tracks formed on a magnetic tape. More particularly, the present invention relates to a video recording apparatus of an automatic track following system (to be referred to as the ATF system hereinafter) wherein a plurality of pilot signals having mutually different frequencies are sequentially recorded together with an information signal, and the reproducing head is tracked along the respective tracks utilizing the pilot signals that are reproduced together with the information signal by the reproducing head.
2. Description of the Prior Art
In a video tape recorder (to be referred to as a VTR hereinafter), video information of one field is recorded in slanted parallel tracks on a magnetic tape by two rotary heads which rotate at a given speed relative to the magnetic tape. In the reproduction mode, the magnetic tape is driven at the same speed as that used in the recording mode, so that the video head correctly reproduces the slanted parallel signals recorded on the respective video tracks.
In order to obtain a still image, frame advance images or reverse frame advance images, the tape is stopped so that the two video heads A and B repetitively scan the corresponding tracks. However, when the tape is actually stopped at a desired position, the scanning track of the head often overlaps more than the desired two adjacent tracks, as indicated by the broken line in FIG. 1. The reproducing head scans across the recorded tracks along the arrow marked x, thereby crossing tracks A2 and A1, corresponding to the video head A and crossing track B1, corresponding to the other video head B. In head A scanning period W1 of a head change-over pulse signal RF-SW shown in FIG. 2B, when the head changes over from track A2 to A1, the desired video signal will not be reproduced at time AL, as shown in FIG. 2A. This lack of signal results in a noise pulse N being included in the reproduced video signal VD (FIG. 2C) of field WI. This is because the video signals are recorded using different azimuth angles in adjacent tracks so as to prevent crosstalk therebetween. If no steps are taken to deal with this lack of signal, a noise bar will be generated in fast forward images and in reverse images. A solution to this problem has therefore been desired.
A first approach to attempt to solve this problem has been to correct the positions of the heads A and B during one field scanning. According to this first approach, the video heads are mounted on a rotary drum using position control leafs such as bimorph elements, so that the head A can be positioned to correctly scan the tracks A1 and A2, and only head B scans the track B1. With this approach, a still image of good quality can be obtained. However, the configuration for mounting the heads A and B becomes complex, resulting in a high manufacturing cost.
A second approach to solving this problem is to control the timing for stopping the tape such that the scanning track of the head overlies two adjacent tracks equally, as shown in FIG. 3. When this mesure is taken, the point AL (FIG. 4A) at which the reproduced video signal is not obtained is shifted to a switching point, or a point close thereto, of the head change-over pulse RF-SW (FIG. 4B). This time point corresponds to a vertical blanking period of a demodulated or reproduced video signal VD (FIG. 4C). Accordingly, even if noise N is generated, such noise is hidden either above or below the actual image frame. Conventionally, this measure has been adopted in a VTR of the CTL tracking type, in which a control pulse (CTL pulse) corresponding to each track is recorded in a drive direction Y of the tape, and tracking control is performed using this CTL pulse. However, a practical working apparatus has not been proposed for use with a VTR of having the ATF system.